Prediction and prophecy are always of special significance in fantasy: if a foretelling is mentioned at all, it is almost certain to be accurate. Delphic ambiguity, Quibbles or mere obscurity of Diction may cloud the issue, but a prophecy, Omen or Portent will never simply be wrong or apply to a different Land, Hero or century. It is a glimpse of perhaps inescapable Fate. Oedipus does not know of and thus cannot avoid his prophesied crimes of parricide and incest. But better-informed attempts to cheat Fate are frequently self-defeating, as with the story of the man who saw Death looking oddly at him, and fled to far-off Samarra (or Persepolis) – there to discover that Death had been surprised to see him in the other city when his next day's appointment with that man was in Samarra. Piers Anthony's Apprentice Adept sequence turns on a self-fulfilling prophecy that one sorcerer, the Blue Adept, will destroy the Red Adept; which Blue eventually does, solely in retaliation for Red's attempts to kill him and thus evade Fate.
Prophetic pronouncements may come from Oracles, as in the Anthony story just cited; in gnomic verses, Riddles and Folklore handed down since ancient times; in Books of prophecy like that of Neil Gaiman's and Terry Pratchett's Good Omens (1990); in Dreams or Visions – often thought to be sent by the Gods; by Scrying; by the casting of Runes; by haruspication, the study of the entrails of a newly slaughtered Sacrifice – chiefly practised by very ancient or Evil prophets (it becomes black comedy in Roger Zelazny's Creatures of Light and Darkness , where the disembowelee is a rival seer with his own interpretation of his entrails); by Necromancy; by use of clairvoyant or precognitive Talent; by the study of Stars and horoscopes (> Astrology); by auspices and augurs; by Tarot, other Cards, or the yarrow-stalks of the I Ching; by sortilege, opening a book at random and interpreting a line or passage as prophecy – as memorably done with the Bible in M R James's "The Ash-Tree" (1904); or even by reading tea-leaves. Numerology is very rarely employed, perhaps because it lacks numinous resonance and is recognized as too easily manipulable.
To preserve both free will and narrative suspense, prophecies tend to become wholly clear only in hindsight. The gods may warn by dropping hints, but they do not compel; the author reserves the right to be untrustworthy and invoke some Quibble, so the coming-about of even a straightforward prediction can still be effective. There is much Story satisfaction in threads of pleasingly fulfilled prophecy, such as are profusely woven throughout J R R Tolkien's The Lord of the Rings (1954-1955); these include prophecies turning on Conditions, like the warning to Legolas against approaching the sea. Fred Saberhagen's The Broken Lands (1968) effectively understates the detailed working-out of an initial prophecy in the climactic action, flattering readers who have traced the thread without heavy auctorial nudging. [CB/DRL]